Paravisual Display (PVD) 747-400

[NSEU]

Just noticed in one of my engineering training books that it says:

"The PVD is enabled by:
*Airplane on ground
*Not Rollout Mode engaged
*LOC Data valid
*Course error less than 45 degrees
*Ground speed more than 40kts"

The last item seems to conflict with the Singapore Airlines 006 incident report which says the PVD unshutters at lineup.

http://www.airdisaster.com/reports/ntsb/ASCAAR-02-01.pdf

The second last item seems to conflict with another manual which says that the displays provide guidance ...

"when the airplane initially turns to within 2.0 degrees of the runway centerline. The guidance stops when the airplane deviation exceeds 3.2 degrees."

Is this a reference to track, rather than heading? Or something else?

Trying to make sense of the information.

All comments welcome :)

[NSEU]

By the way, do the PVD's have to be selected off after takeoff to remove the memo messages?

Thanks.

[rudderrudderrat]

Hi NSEU,

My old notes say:
"PVD unshuttered -
PVD selected on, within valid localizer region, within 45 degs of runway heading, and on ground.
"barber pole" rotates in direction of runway centreline.

Shuttered PVD off -
not within valid localizer region or within 45 degs of runway heading
above 5 ft rad alt
selected PVD source invalid"

It was available from standing still until airborne (40 kts is a red herring)
It makes sense to have the memo message displayed if the PVD is turned on - else you wouldn't know whether it was really on when it wasn't displayed (airborne say for Auto Land with possible manual roll out)

[spannersatcx]

one of the airlines we look after has them deactivated!

[eckhard]

Hi NSEU,

rudderrudderrat has it about right, except

It makes sense to have the memo message displayed if the PVD is turned on - else you wouldn't know whether it was really on when it wasn't displayed (airborne say for Auto Land with possible manual roll out)

As far as I'm aware, the PVD turns itself off after liftoff and is not available in flight. It is intended purely for guidance during the take-off roll.

So the reason to have the STATUS message is that after you've turned it on (and adjuted the brightness) you then know that it will unshutter again when you line up and achieve the requirements listed by rudderrudderrat:

"PVD unshuttered -
PVD selected on, within valid localizer region, within 45 degs of runway heading, and on ground.

[NSEU]

Thanks, gents!

As far as I'm aware, the PVD turns itself off after liftoff and is not available in flight. It is intended purely for guidance during the take-off roll.

On this point, I was wondering if it actually turns itself off, or the shutters just close (as happens when the system is armed prior to takeoff, and before entering the runway)

"PVD unshuttered -
PVD selected on, within valid localizer region, within 45 degs of runway heading, and on ground.

The manuals say that this "ground" signal is actually a "Rad Alt < 5feet" signal sent to the Flight Control Computer which then sends this and other data to the Para Visual Display Computer. The "in air" logic is actually RA>5 feet AND groundspeed > 80kts. I can't see the sense in the 80kt logic, but this rather low airspeed logic appears in a number of different systems.

[rudderrudderrat]

Hi eckhard,
It is intended purely for guidance during the take-off roll.
On the L1011 we could do a manual Roll Out in 75m RVR mid point provided the PVD was available.
From memory, I think on the 747-400 we were restricted to 100m RVR mid point with manual Roll Out & with PVD - else with no PVD it was 125m.

[NSEU]

A captain told me yesterday that the PVD completely shuts off after takeoff. i.e. Memo messages removed without manual intervention.

This may mean you can't test or "arm" it in flight.

Not quite how I thought it worked.

[eckhard]

Hi rudderrudderrat,

Not sure which year you are referring to for the 747-400 but since 1997 I'm sure we have never used the PVD for landing.

The minimum RVR for take-off on the -400 is 150m (or 100m with PVD if notified in the take-off performance manual or CARD).

The minimum RVR for landing is 100m/100m/adv. There is no allowance for PVD.

Re-reading the tech manual, it does seem theoretically possible to use the PVD for landing, but you would have to push the PVD selector button below 5ft RA for it to unshutter. You cannot 'arm' it in the air.

Interesting to hear that you used it for landing on the TriStar.

[NSEU]

Re-reading the tech manual, it does seem theoretically possible to use the PVD for landing, but you would have to push the PVD selector button below 5ft RA for it to unshutter. You cannot 'arm' it in the air.

Eck, does your tech manual mention the Rollout PVD inhibit found in our manuals?

Rollout mode, according to autopilot/FD notes in one 747-400 manual, includes LOC mode (ROLLOUT un-annuciated) on the PFD, so the PVD may be inhibited during Autoland and FD-guided landings.

[rudderrudderrat]

Thanks for the correction - I must have confused TriStar & 747-400 Low Vis Landing Ops. Please see:
http://www.pprune.org/engineers-technicians/17892-para-visual-display-query.html

[eckhard]

RRR, No problemo.

NSEU, I suppose if the roll mode changes from LOC to ROLLOUT, that would inhibit the PVD, so maybe it is not theoretically possible to use it for landing (autoland); however, if the autopilot was not engaged wouldn't the roll mode remain in LOC, thus enabling the PVD?

I'm not suggesting that this would be a good idea, given that in these RVRs you would want to autoland anyway, but just speaking theoretically?

[NSEU]

I've just seen a YouTube video of a 777 autolanding. The PVD comes alive during rollout after A/P disengagement.

It wasn't armed after touchdown. If the system is switched off completely after T/O (memo message/s removed), how did it rearm itself with an in-air inhibit?

Also, I experienced some (reproduceable) unexplained behaviour on a 747-400 today. If I pull all MMR CBs and arm a PVD, the PVD runs through its selftest, then the shutter remains open! Randomly, it scrolled left or right at various speeds or in some cases, stayed still. This weirdness, however, was inhibited during IRU alignment and in ATTitude mode (not sure about full NAV).

I'd love to know which committee designed this system :}

Cheers

[wiggy]

I've just seen a YouTube video of a 777 autolanding. The PVD comes alive during rollout after A/P disengagement.

It wasn't armed after touchdown. If the system is switched off completely after T/O (memo message/s removed), how did it rearm itself with an in-air inhibit?

Different aircraft, different logic.

On the 777, unlike the 744, you can rearm the PVDs once airborne (and you get the memo messages again), they will then unshutter on touchdown.

[safetypee]

IIRC the PVD resulted from research by the Blind Landing Experimental Unit (BLEU) in conjunction with Smiths Industries and Hawker Siddley for use in the Trident aircraft. I assume that BA (BOAC/BEA) provided some evaluation crews.

Further research included vertical guidance – see the installation in HS 748 G-ASJD (later XW750 BLEU) HS748 G-ASJT - a photo on Flickriver (http://www.flickriver.com/photos/egbj/5359654355/#large)

There was also some later research using LED dot matrix systems for flare guidance.
Also IIRC, the military considered some applications of the concept for low altitude roll attitude awareness with a strip display around the windshield.

[NSEU]

*Ground speed more than 40kts"

After further reading, this logic seems to apply only to test (but it's not clear if this is the CMC Test or the quick left/right confidence test during arming).

Thanks for the updates, guys :ok:


British Airways cockpit landing into foggy Gatwick - YouTube (http://www.youtube.com/watch?v=ZRWlkFKENLA)

Looking at this 777 autoland video, the PVD inhibit during rollout only seems to operate with the A/P engaged (or are the F/D modes changed/erased when you disconnect the A/P?)

[NSEU]

Another question, if I may...

What indications would the PVD show at point "A"? Rolling right to indicate turn right to intersect the runway centre line? Or rolling left to continue turning (to line up with the centre line?) The former is more like raw data, the latter would be more like FD guidance when intersecting the loc.

http://www.iinet.net.au/[email protected]/PVD1.JPG

[Pontius]

It would roll left to indicate the centreline is over to the left and that you should go left to get back on centreline. I suggest this is more like raw data i.e. the localiser needle is left so you need to fly left to bring it back to the middle.

It's not bright enough to roll right to intercept the centreline. It's not a flight director that is taking into account turn rates, wind etc, all it's doing is showing you where the localiser is; localiser left, it'll roll left to tell you to go that way to get back on centreline.

Having maligned its simplicity I have to say it is very intuitive and works brilliantly :)

[Spanner Turner]

Exactly what Pontius said !!

:ok:

[Aluminium shuffler]

I have never seen PVD, being a 73 driver. Is it displayed for the T/O runway regardless of nav selections? I'm curious because the 73 EFIS and NG have the ILS needles on the PFD, as long as you select an ILS freq on the nav sources, and the LOC needle will seemingly do the same job. Is it simply a system that gives better peripheral and faster/quicker recognition needed because of the higher cockpits of the wide bodies resulting in greater slant ranges for seeing the runway lighting, given that we would operate to the same departure minima?

[wiggy]

On the T7/744 you need to have the freq and LOC course hard tuned on the NAV RAD page.

Is it simply a system that gives better peripheral and faster/quicker recognition needed because of the higher cockpits of the wide bodies resulting in greater slant ranges for seeing the runway lighting,

I guess the logic is something like that. the display sits just at the bottom of your peripheral vision and as Pontius says it's very intuitive to use

All that said our latest T7s are being delivered without them, story goes they (well the one's we use) are expensive to maintain and in reality are rarely used in anger.

[rudderrudderrat]

Hi Pontius,
It's not bright enough to roll right to intercept the centreline. It's not a flight director that is taking into account turn rates.....
I beg to differ.
During line up at taxi speed, the TriStar PVD would be steady with an intercept heading towards the centre line and then show a turn command to align with the centre line.
It was certainly more sophisticated than a simple localiser deviation display, and it considered:
airplane yaw rate
cross body acceleration
localiser deviation
localiser deviation rate.

[Winnerhofer]

No self-respecting airline can be without this option.
It has unfortunately disappeared on the B748,B777x and B788.
In Airbus parlance it's called PVI but only one indicator on LH-side and this too is no longer on the option list of A388, A350 and A320 Neo.

[Aluminium shuffler]

Thanks, Wiggy.

Would I be right in y understanding that they rotate fast the greater the displacement from the centre-line?

It seems a shame to remove or omit kit that the pilots have a clear and unanimous liking of, but that's what happens when engineers and accountants have absolute dictat over cockpit design... Engineers can come up with wonderful solutions to problems, but only pilots can know what works and what doesn't for us. I get the impression that modern test pilots are told merely to prove the design flies, and not allowed to feed back recommendations of what would make it better for line pilots and crew. :(

[By George]

My old company deactivated the PVD on the 744 for the simple reason they were never needed. Tragically the one time they might have saved the day in Taiwan, the crew failed to recognize the off-set indication.
We were CAT3b on the 744 and the R/W centre lights were more than adequate. The recency requirements in the Sim and the fact it was never really needed, killed it off. Maybe Boeing agrees. I found it very useful for an engine failure in low vis but that is all. Sometimes the men in white coats can have too many gadgets. (my new car suffers from Geek Overload and is driving me nuts).

[EEngr]

wiggy (http://www.pprune.org/members/28194-wiggy):

are expensive to maintainQuick survey. Are PVDs (where installed) still largely implemented as electro-mechanical displays? Or have they gone to something like a one line graphic LCD?

[By George]

Engr, On the 744 they were electro-mechanical. Quite noisy going on test with a 'click clack' sound. The 'blind' was yellow and black stripes.

[Winnerhofer]

Scroll down to pic #2 :
744 Gallery 04 (http://www.aerowinx.com/html/gallery04.html)
http://www.aerowinx.com/assets/pics/autogen/clearpixel.gifhttp://www.aerowinx.com/assets/pics/autogen/clearpixel.gif

[EEngr]

So, if their elimination is an issue of maintenance expense and this is still a valued instrument, it surprises me that someone hasn't come out with a 'digital' barberpole display. Quite simple to to with a one line graphical LCD properly backlit. No moving parts and no noise.

Unless you like the noise. We could easily emulate that.:8

[Dan Winterland]

My old company deactivated the PVD on the 744 for the simple reason they were never needed. Tragically the one time they might have saved the day in Taiwan, the crew failed to recognize the off-set indication.

One of them did - the F/O sitting on the jump seat. He mentioned it to the Captain, but was dismissed.

I used to fly 744s with PVDs fitted, but never used them in anger. Most Capatains chose not to use them as many pilots don't find the dispaly intuitive.

The PVI is an option on FBW Airbus and (I gather) it is an LCD display. But very few operators have taken up the option.

[henry_crun]

I was at Smiths, working in the design labs, CH3, and can recall seeing our barbers pole type Para-Visual Director which was invented by Mr Majendie, I think he was one of our test pilots.

Photo as Fig 1 in here:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19690005146_1969005146.pdf

Correction - Mr Majendie was a de Havilland Test Pilot, which would figure because we were doing the DH Trident Autoland. Saw him once when he visited Test Equipment lab.